In the case of bicycles having a chain driven drive train and having an individual chain wheel on the front crank arrangement, the chain is driven via said individual chain wheel. For this purpose, during driving, the individual chain wheel engages in sections by means of the teeth thereof in the chain and interacts in a known manner therewith. The advantage of a bicycle front crank arrangement with an individual chain wheel in comparison to a front crank arrangement with a plurality of chain wheels consists in that fewer components are installed. For example, in such an arrangement, it is possible to dispense with further chain wheels on the front crank arrangement and with a derailleur. Fewer components and an associated reduction in the number of gear changing operations lead at the same time to such an arrangement being less prone to gear changing errors.
However, arrangements of this type also dispense with securing components which secure the drive chain on the individual chain wheel and inhibit the chain from jumping under load radially outward over the teeth which are in engagement. For this reason, it is attempted, in the case of individual chain wheels, to form the teeth in such a manner that the geometry of the teeth prevents the chain from jumping off or over. For this purpose, the teeth of individual chain wheels generally have load flanks which are as steep as possible.
An individual chain wheel for a bicycle front crank arrangement is known, for example, from German laid open application DE 10 2012 023 819 A1. The document describes an individual chain wheel for engaging in a drive chain, the individual chain wheel comprising a plurality of teeth. The plurality of teeth includes a first group of teeth and a second group of teeth which is arranged in an alternating manner between the first group of teeth. The two groups of teeth are formed here with differing material thickness with respect to the corresponding chain gaps of the drive chain in order to permit secure engagement of the teeth of the individual chain wheel in the drive chain. As already described previously, this arrangement also has teeth with relatively steep load flanks in order to inhibit the chain from jumping under load outward over the teeth.
Teeth formed in such a manner and having steep load flanks may have a wear induced abrasion of material caused in the load flanks in a region of the greatest loading by the rollers of the drive chain over the service life of the chain wheel. In other words, the roller digs further into the respective load flanks over the duration of the loading. As a result thereof, edges are produced in the load flanks of the teeth, which edges may impede and/or block the slipping of the drive chain or of the rollers. In this case, reference is made to “chain suck” occurring.
FIG. 35 shows by way of example with dashed lines various states of the continuous abrasion of material on the load flanks of the teeth of known individual chain wheels, starting from an initial state shown by a solid line. The production of an edge over the duration of the loading is visible here, the edge, as described previously, constituting an obstacle for the respective roller and therefore impeding the slipping of the drive chain.
This negative effect occurs in particular in the case of bicycle front crank arrangements with individual chain wheels. The latter are loaded comparatively more strongly than the respective chain wheels of a front crank arrangement with a multiple chain wheel arrangement since the chain interacts continuously with one and the same chain wheel of the front crank arrangement during operation.
It is therefore an object of this disclosure to provide an individual chain wheel for a bicycle front crank arrangement, in which abrasion of material in the load flanks of the teeth by the rollers, which act thereon, of the drive chain does not lead to blocking of the drive chain, and therefore a substantially unimpeded slipping of the drive chain is still possible under wear even after operation for a relatively long time. An additional object may involve the prevention of the rollers which are in engagement from jumping under loading radially outward with respect to a central axis of the chain wheel over the teeth which are in engagement.